Distance measuring device and method for determining a distance, and suitable reflecting body

ABSTRACT

A distance measuring device and method for determining distance, and a suitable reflective member are provided. The distance measuring device includes analysis electronics and a sensor device, which has at least one coupling probe for feeding a transmission signal into a line structure. A reflective member is disposed in the line structure which has a base plate with an attached collar forming a cup-shaped element, and a feed block with a recess into which the collar plunges. The recess has a sealing ring which produces airtightness with the collar, wherein the attached collar is provided on the front face with a plastic plate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a filing under 35 U.S.C. §371, which claims priorityto and the benefit of the filing date of PCT Application No.PCT/EP/2008/003437, filed Apr. 28, 2008 and German Patent ApplicationNo. DE 10 2007 020 046.5, filed Apr. 27, 2007, the subject matter ofeach of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a distance measuring device, as well asto a method for determining a distance and to a suitable reflectivemember.

Conventional distance measuring devices are used among other things, forexample, for detecting the piston position of fluidic linear drives andpneumatic and hydraulic cylinders. The detection of the piston positionon cylinders can be implemented both discretely, i.e. at discretepoints, and continuously, i.e. constantly during operation.

A discrete piston position determination is generally required in orderto report back the implementation or end of a piston movement to asequence control system (e.g. SPS) in order to thus be able to initiatethe next sequence step, for example.

Predominantly used for this purpose are sensors or sensor devicessensitive to magnetic fields which detect the magnetic field of apermanent magnet which is located on the cylinder piston. The sensorsused here are fitted externally to the cylinder tube of the pistoncylinder. If the piston moves into the detection range of this type ofsensor, the latter recognizes the presence of the cylinder pistonthrough the cylinder tube. For this, the use of non-ferromagneticmaterials is predominantly required and so restricts the structuralproperties and applications of the drive.

If, however, a different position of the piston is detected, the sensormust be correspondingly mechanically adjusted. For each position to bedetected, in addition a further sensor must consequently be fitted,accompanied by the associated additional material, fitting, adjustmentand installation costs. This generally takes place at the customer'spremises. Here the cylinder is often already integrated into a machinewhich is difficult to access, and adjustment of the switching distancesby mechanically moving the externally fitted magnetic switches is nolonger possible.

Furthermore, for these externally fitted sensors additional installationspace is required. So that the accessibility and robustness of thesensor can be guaranteed, additional structural complexity is oftenrequired.

These types of sensor are predominantly in the form of sensors sensitiveto magnetic fields and are known as Reed switches, magnetoresistive(MR), giant magnetoresistive (GMR), Hall switches or magnet-inductiveproximity switches.

Complex coordination of the magnet to the sensor device is required fordetection of the magnetic field. Moreover, with this measuringprinciple, the possible applications are restricted by interferingstatic and dynamic magnetic fields (EMV, field of a nearby cylinder) andthe temperature characteristics of the sensor.

For the continuous measurement of the piston, position measuring systemsare generally used which function potentiometrically,magnetrostrictively according to the LVDT principle (Linear VariableDifferential Transformer) or according to the ultrasound principle. Withthese systems the piston position is emitted continuously andpredominantly as an analog voltage signal. Sensors according to the LVDTprinciple always require a reference path when switched on.Magnetostrictive sensors are fitted either externally onto the cylinderor into a hollow piston rod. Both fitting possibilities meansubstantially increased complexity, are prone to interference or weakenthe stability of the drive in the case of the hollow piston rod.Ultrasound sensors are only suitable to a limited degree for the pathmeasurement in pneumatic and hydraulic cylinders because the measuringaccuracy changes with the cylinder pressure. Incremental pathmeasurements are also known as a supplement to these systems. Thesesystems are implemented, for example by the coding of the piston rod,and so can only be used for the relative path measurement.

Neither the continuous nor the discrete piston position determinationcan be integrated into a cylinder or can only be so with substantialstructural complexity and the associated high costs. The substantialstructural complexity is due to the fact that all of the establishedsensor principles described must be adapted to the correspondingcylinder length because the principles have a detection range which istoo short.

The ideal path measuring system for determining the piston position inpneumatic and hydraulic cylinders has the following properties:

-   -   continuous, absolute path measurement with an accuracy of 100 pm        for positioning the piston    -   total integration of the sensor with analysis electronics into        the cover of the cylinder    -   switching distances should be adjustable externally via an        electronic interface (teach-in capability)    -   a universally applicable sensor, independently of the cylinder        length    -   measurement results independent of pressure, oil and humidity in        the cylinder    -   reliable measurement results, e.g. up to 10 bar pressure and 6        m/sec piston speed in the pneumatic cylinder.

In practice, known measuring systems patent application have thefollowing problems for cylinders with a large diameter (>50 mm):

-   -   The plastic ring for the piston stop and the antenna retainer is        very large. These plastic parts are only available up to a        diameter of max. 60 mm as ready-made items. For larger diameters        expensive custom-built models are required.

Moreover, plastic absorbs water over time or releases water according tothe conditions of use, and in this way changes the measuring conditions.The measurement results then become inaccurate and no longer correspondto the specification.

Classic end position damping e.g. of the pneumatic piston can only beachieved by the moved brake ring made of plastic at the expense ofmeasuring accuracy.

Further disadvantages of known measuring systems are:

that the conventional pistons in the pneumatic cylinder are relativelythin and generally have a magnetic ring in the center in order to enableoperation with externally fitted Reed switches. These pistons do notform an ideal reflective member for an electromagnetic wave. Part of theelectromagnetic wave passes over the piston into the functional space ofthe cylinder lying behind this, returns with a time delay and interfereswith the useful signal. This substantially worsens the measuringaccuracy. Furthermore, there are pistons which are made entirely ofplastic. These pistons do not constitute a reflective member at all forthe electronic wave. The method described, for example, in DE 102 05904.7 then no longer works at all.

Furthermore, a disadvantage of a piston stop in the cover made ofplastic is that the plastic is settled by frequent piston impacts and sothe physical conditions in the functional space of the cover change forthe high frequency sensor. Moreover, the measuring accuracy worsens.

In addition, with smaller cylinder diameters it is very difficult tointegrate the discrete electronics into the cylinder cover. Part of theelectronics must then complexly be accommodated externally, e.g. on thecylinder wall.

A device for determining the position of a piston in a pneumaticcylinder is known from U.S. Pat. No. 4,588,953. During the movement ofthe piston a microwave signal is delivered into the cavity which isbordered by the outer wall of the cylinder and the piston. The reflectedmicrowave signal is received and processed in order to determine theposition of the piston.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one embodiment, a distance measuring device isprovided that includes analysis electronics and a sensor device, whichhas at least one coupling probe for feeding a transmission signal into aline structure. A reflective member is disposed in the line structurewhich has a base plate with an attached collar forming a cup-shapedelement, and a feed block with a recess into which the collar plunges.The recess has a sealing ring which produces airtightness with thecollar, wherein the attached collar is provided on the front face with aplastic plate.

In accordance with another embodiment, a method for determining adistance using a distance measuring device is provided. The methodincludes providing a line structure reflection which has a feed blockwith a feed region which connects a high frequency (HF) transceiver to adielectric restraint system with a coupling probe via a waveguide. Themethod further includes providing a reflective member with a base platewith an attached collar for forming a cup-shaped element, and measuringa distance between a feed point defined by the coupling probe and thereflective member, wherein at least two transmission signals aselectromagnetic waves with different frequencies are coupled via thecoupling probe.

In accordance with yet another embodiment, a reflective member for adistance measuring device having analysis electronics and a sensordevice which has at least one coupling probe for feeding a transmissionsignal into a line structure and with a reflective member disposed inthe line structure which has a base plate with an attached collarforming a cup-shaped element, and a feed block with a recess into whichthe collar plunges is provided. The recess has a sealing ring whichproduces airtightness with the collar, wherein the attached collar isprovided on the front face with a plastic plate. The reflective memberis configured to reflect a high frequency (HF) signal and has a baseplate with an attached collar for forming the cup-shaped element.

BRIEF DESCRIPTION OF THE DRAWINGS

By means of the following drawings, various embodiments of the distancemeasuring device according to the application are illustrated.

FIG. 1 shows a sectional illustration of the distance measuring devicein an integrated line structure;

FIG. 2 shows perspectively an exploded view of the distance measuringdevice according to various embodiments (left-hand side) and of thedistance measuring device according to various embodiments in theassembled state (righthand side);

FIGS. 3-9 show further sectional illustrations of different embodiments(or portions thereof) of the distance measuring device;

FIG. 10 shows a block diagram of the analysis electronics;

FIGS. 11 and 12 show line structure arrangements according to the priorart; and

FIG. 13 a-d shows a sequence of the reflective member at an end positionof the reflective member.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention provide a distancemeasuring device, a reflective member and a method for determining thedistance which enable continuous and therefore discretisable distancedetermination, simple handling and versatile possibilities for use.

According to the various embodiments, it is made possible by thegeometric design of the reflective member for the coupling probe toplunge without any contact into the interior of the reflective member,in particular within the collar, upon deflection of the reflectivemember. Displacement of the position of the coupling probe is preventedand the measuring accuracy retained. Due to the presence of the collarit is possible for the deceleration process of the reflective member tobe implemented with a plastic ring which does not effect the distancemeasurement because the plastic ring is not located within thereflective member.

Furthermore, according to various embodiments a line structure isprovided which has a feed block with a feed region which connects an HFtransceiver to the coupling probe via a waveguide with dielectricrestraint systems. With this arrangement, total integration of thecoupling probe with the analysis electronics in the cylinder cover ispossible. Therefore, additional parts to be fitted externally are notrequired. The corresponding switching distances can be adjustedexternally via the analysis electronics by means of an electronicinterface, The distance measuring device according to the applicationcan basically be used universally independently of the cylinder length.Moreover, it has been shown that the measurement results are reliablycorrect independently of the pressure, oil and air humidity in thecylinder.

According to various embodiments a distance measuring device and amethod for determining a distance is made available, the sensor devicehaving a high frequency feed system which serves to measure a specificdistance, for example in a line structure (a line structure being e.g.the interior of the pneumatic cylinder=circular hollow conductor) byradiating and receiving waves, the feed system being integrated into theline structure, for example. Upon the basis of this integration of thefeed system it is possible for the distance measuring device to have asmall structure and for practically no or only slight structuralalterations to be required. Therefore, the overall structure of thedistance device can have a clean, sleek design due to dispensing with afitting possibility for external sensor devices and does not effect theexternal appearance. With the distance measuring device according tovarious embodiments economy of installation is achieved because thepre-fabricated cylinder only has one connection cable for control anddata collection. According to methods of various embodiments the lengthof the line structure is measured up to a short circuit (e.g. piston asreflective member with the pneumatic and hydraulic cylinder) which isalso moveable. The transmission signal provided is fed into a linestructure and preferably reflected by a short circuit (=cylinderpiston). In this way the measurement of the distance between the feedpoint defined by the coupling probe and the short circuit of the linestructure is implemented. The distance to be measured here isimplemented by measuring the phase difference between the transmittedand the received signal.

More specifically, the arrangement may be provided as follows:

The RF feed system comprises a coaxial monopole stimulation system. Byfeeding a transversally electromagnetic wave (TEM wave) in the coaxialinlet region (3) a circular hollow conductor wave with thecharacteristic E field type of the E01 wave is stimulated by themonopole system. This wave propagates within the running cylinder in theaxial direction. If this wave strikes a reflective member (within thepneumatic and hydraulic cylinder the piston), the wave is reflected andconverted and conveyed into the coaxial line system via the stimulationsection (monopole). The monopole feed comprises a 3-stage coaxialtransformation stage (2) with a dielectric restraint system (1), forexample, made of PPS Gf 40 material, for positioning and pressurestabilisation.

With cylinders with a large diameter the dielectric restraint system isimplemented partially in the form of dielectric supports. The piston endstop is formed by a base plate with an attached collar for forming acup-shaped part (3) made of aluminium which is fitted as an end pieceonto the piston. The cup is formed here such that the antenna plungeswithout any contact within the cup upon impact. A plastic plate (4) isaccommodated on the front face of the cup in order to enable a softimpact. This cup additionally serves as a reflective member for thetransmitted electromagnetic wave. In order to achieve ideal reflectionconditions, around the periphery of the reflective member so-called“corregations” (5) are provided. These are milled grooves whichconstitute a short circuit for the electromagnetic wave. Depending onthe number of grooves an almost perfect short circuit can therefore beproduced. In practice 2 grooves are sufficient. The depths of thegrooves correspond to a quarter of the wavelength of the transmissionfrequency of the electromagnetic wave used.

Further embodiments of the reflective member consists of it being ableto be designed in order to implement the function of end positiondamping. Without the end position damping the piston would strike thecover without any deceleration. This leads to jerks and can cause damageto the drive system. The classic end position damping is achieved by thepiston rod projecting over the piston towards the sensor and beingprovided with a conically extending plastic attachment. The counterpiecein the end cover forms a plastic ring, the internal diameter of which isof such a size that the piston rod can plunge with the conicallyextending plastic attachment. If the internal diameter of the plasticring corresponds to that of the external diameter of the conical pistonrod attachment, the piston is decelerated. In order to enable thecylinder to start up smoothly following a deceleration process, theplastic ring is mounted in the cover so that it can move e.g. a fewmillimetres axially. If the piston starts up again following adeceleration process, it takes the plastic ring with it up to the stopof the latter. Due to the kinetic energy which the piston then has,there is a gentle jolt and the plastic ring is released from the conicalplastic attachment of the piston rod. The deceleration process issupported by an air exchange between the cover and the cylinder spaceadjustable by means of a screw.

The disadvantage for the HF path measuring system is that the movementof the plastic ring within the cover space changes the physicalcircumstances for the sensor and the measuring accuracy consequentlyworsens substantially. Basically the classic end position damping canalso be implemented with the configurations described herein. Theplastic ring sits in the cover and the conical extension of the pistonrod is provided on the reflective member. The movement of the plasticring is now masked by the cup, i.e. the sensor signals can no longer beinterfered with by the antenna plunging into the cup due to the movementof the plastic ring. Another embodiment is achieved when the work schemeis reversed. The moveable plastic ring is now fitted onto the outersurface of the cup and the cover plunge surface is formed conically andcoated in plastic. The movement of the ring over the reflective memberdoes not effect the electromagnetic wave because the plastic ring is nolonger located in the vicinity of the antenna. Likewise, the pneumaticpressure compensation is provided in the cover. All of the plastic partsdirectly next to the monopole antenna are made of a plastic materialwith low water absorption such as e.g. PPS Gf 40.

The whole pneumatic cylinder between the piston rod and the rearwardcover is observed during the process introduced e.g. as a circularhollow conductor. According to the geometric dimensions of the cylinderthe transmission frequency of the sensor is chosen such that monomodalpropagation of the electromagnetic wave (in the example in the E01 mode)is possible. Stimulation of hollow conductor modes of a lower order isprevented by the geometry of the feed. The stimulation of theelectromagnetic wave in the cylinder is implemented e.g. via a monopole(=antenna) as described. According to the reflectometer principle thewave propagates in the circular hollow conductor (=pneumatic cylinder)and is reflected on the piston (=short circuit). In order to be able tomeasure the distance between the piston and the sensor continuously, thetransmission signal is modulated. This can take place in the form of afrequency modulation or by analyzing the phase difference between thetransmitted and the received signal with a number of frequencies. Thetransmission frequency is generally between 100 MHz and 25 GHz, butother frequencies may be used.

The use of a dielectric secondary ring serves as a stop safeguard forthe moving reflective member and is taken into account with theelectromagnetic design of the feed system.

It has proven to be particularly advantageous if the line structure is acircular hollow conductor, preferably a cylinder with a piston, as areflective member. A circular hollow conductor of this type can be forexample a pneumatic cylinder or a hydraulic cylinder. The disadvantageswhich have been experienced to date are therefore dispelled inparticular for these applications.

Due to the presence of boreholes in the feed block into which therestraint system, the coupling probe and the coaxial feed region can beinserted, simple fitting is provided and the whole distance measuringdevice can be integrated almost any way into existing line structures.

It has also proved to be advantageous if the coupling probe is designedas a monopole stimulation system and the electromagnetic wave feed isimplemented coaxially so that a circular hollow conductor wave can befed in and be converted to the monopole by means of a multi-stagecoaxial transformation stage. By means of the multi-stage coaxialtransformation stage, which can have a level base area on which anelectrically conductive cylinder is provided in the center, and to whichan electrically conductive pin is attached as an inner conductor of thecoaxial feed, it is possible for the whole feed to be implementedsimply.

The restraint system comprises dielectric, e.g. lexan, and is used forthe positioning of the coupling probe within the cylinder. Furthermore,it provides the required mechanical stability when subjected to pressure(e.g. 10 bar in the pneumatic cylinder). During series production thefeed block can be produced particularly cost-effectively by the monopolestimulation system being inserted into the cylinder cover and thedielectric restraint system connecting said system to the cylinder coverby means of the plastic injection method.

An electromagnetic wave in the high frequency range of between 100 MHzand 25 GHz also may be fed in. Dependently upon the dimensions andmeasurements of the cylinder used as the line structure and the wavemode, an appropriate frequency is chosen which is above the lower limitfrequency of the wave mode used.

In FIG. 1 the distance measuring device 11 according to variousembodiments is illustrated with a line structure 1 and a feed block witha feed region 2, the feed region having a coupling probe 3 via adielectric restraint system 5 with the waveguide 7. In addition, thedielectric secondary ring 9 is illustrated which serves on the one handas a mechanical stop safeguard and is designed as a secondary adjustmentand radiation system.

The respective components of the distance measuring device according tovarious embodiments are illustrated more clearly in FIG. 2, withcomponents such as the feed block with the feed region 2 beingreproduced in an exploded view. It can also clearly be seen that thedielectric restraint system holds the coupling probe 3 in the form of amonopole stimulation system which includes a pin which can beaccommodated in a coaxial waveguide. In addition the dielectricsecondary ring 9 is shown. Likewise, the reflective member 13 with theattached collar for forming a cup-like element, the base plate of whichadvantageously has a groove structure, is shown.

For better understanding the mode of operation of the distance measuringdevice according to various embodiments and of the method fordetermining the distance will be described more clearly.

The feed system comprises a coaxial monopole stimulation system. Byfeeding a transversally electromagnetic wave, i.e. TEM wave in thecoaxial feed and input region 3, by means of the monopole system acircular hollow conductor wave with the characteristic E field type ofthe E01 wave is stimulated. This wave propagates within the runningcylinder in the axial direction. If this wave strikes a reflectivemember, i.e. in the pneumatic and hydraulic cylinder the piston, thewave is reflected and converted by the stimulation section (monopole)into the coaxial line system and conveyed on to a HF transceiver(transmitting and receiving unit). The monopole feed comprises amulti-stage coaxial transformation stage as a coupling probe 3 with adielectric restraint system 5, for example, made of PPS Gf 40 material,for positioning and pressure stabilization. With cylinders with a largediameter the dielectric restraint system is partially designed in theform of dielectric supports. The piston end stop is provided by means ofa cup-shaped part 6 made e.g. of aluminium, which is fitted on thepiston as an end piece. Here the cup is designed such that upon impactthe antenna plunges without contact inside the cup. A plastic plate 12is accommodated on the front face of the cup in order to enable a softimpact. This cup serves additionally as a reflective member for thetransmitted electromagnetic wave.

In order to achieve ideal reflection conditions so-called “corregations”8 have been provided around the periphery of the reflective member.These are milled grooves which constitute a short circuit for theelectromagnetic wave. Depending on the number of grooves an almostperfect short circuit can therefore be produced. In practice two groovesare sufficient. The depths of the grooves correspond to approx. aquarter of the wavelength of the transmission frequency of theelectromagnetic wave used when air is located in the grooves. The depthof the grooves can be shortened substantially if the latter are filledwith dielectric e.g. teflon. In practice dielectric rings will beinserted.

A further embodiment of the reflective member is such that it can beformed to enable the execution of the function of end position damping.Without end position damping the piston would strike the cover withoutany deceleration. This leads to jolts and can cause damage to the drivesystem. Classic end position damping is implemented in that the pistonrod projects over the piston towards the sensor and is provided with aconically extending plastic attachment. The counterpiece in the endcover forms a synthetic ring the inner diameter of which is of a sizesuch that the piston rod can plunge in with a conically extendingplastic attachment. If the inner diameter of the plastic ringcorresponds to that of the outer diameter of the conical piston rodattachment, the piston is then decelerated. In order to enable thecylinder to start up smoothly following a deceleration process, theplastic ring is mounted in the cover such that it can move axially e.g.a few millimeters. If the piston starts up again following adeceleration process, then it carries the plastic ring with it up to thelatter's stop. By means of the kinetic energy which the piston then hasthere is a gentle jolt and the plastic ring is released from the conicalplastic attachment of the piston rod. The deceleration process issupported by an air exchange between the cover and cylinder space whichcan be adjusted by means of a screw. The disadvantage for the HF pathmeasuring system is that the movement of the plastic ring within thecover space changes the physical circumstances for the sensor and inthis way the measuring accuracy is substantially worsened. Classic endposition damping can also be implemented with the proposedconfiguration. The plastic ring sits in the cover and the conicalextension of the piston rod is implemented on the reflective member. Theadvantage of this solution is that the movement of the plastic ring isnow masked by the cup, i.e. the sensor signals are no longer interferedwith by the plunging of the antenna into the cup by the movement of theplastic ring.

An equally advantageous embodiment is achieved if the work scheme isreversed. The moveable plastic ring is now fitted onto the outer surfaceof the cup and the cover plunge surface is formed conically due to theapplication of a plastic ring. The movement of the ring over thereflective member does not effect the electromagnetic wave because theplastic ring is no longer located close to the antenna.

All of the plastic parts directly adjacent to the monopole antenna aremade of a plastic material with low water absorption such as e.g. PPS Gf40.

An account of the method according to various embodiments will now bygiven by means of a pneumatic cylinder. Here the whole pneumaticcylinder between the piston rod and the rearward cover e.g. as acircular hollow conductor will be considered. The transmission frequencyof the sensor is chosen according to the geometric dimensions of thecylinder such that monomodal propagation of the electromagnetic wave (inthe example in the E01 mode) is possible and that the stimulation ofhollow conductor wave modes of a higher order is prevented. Thestimulation of hollow conductor modes of a lower order is prevented bythe geometry of the feed. Stimulation of the electromagnetic wave in thecylinder takes place e.g. via a monopole in the way presented. The wavepropagates in the circular hollow conductor (=pneumatic cylinder)according to the reflectometer principle and is reflected on the piston(=short circuit). In order to be able to measure the distance betweenthe piston and the coupling probe continuously, the transmission signalmust be modulated. This can take place in the form of a frequencymodulation. In order to achieve a high distance resolution here a largefrequency shift is required however. In practice transmission of a CWsignal is more advantageous, e.g. with three different frequencies (forexample: 5.8 GHz, 6.0 GHz, 6.2 GHz) in order to establish a cleardistance range with respective subsequent analysis of the phasedifference between the transmitted and received signal as a highlyaccurate measured value for the distance between the coupling probe andthe piston. The number of frequencies to be used and the position of thelatter is first and foremost dependent upon the maximum distance to bemeasured and the required error tolerance in relation to the phase anglemeasurement. In general, with a small frequency difference between twomeasured frequencies the maximum measurable distance is greater, but thedifference between two consecutive periods requires greater accuracy ofthe phase angle measurement than with a greater frequency difference.Resistance to interference is therefore higher with greater differencesbetween the individual measuring frequencies.

If a large measuring range with sufficient resistance to interference isto be measured, a number of measuring frequencies with a suitablefrequency position are required. For this reason frequency pairs bothwith a small difference in transmission frequency (large measuringrange) and with a large frequency difference (interference resistance)are then used.

The position accuracy is substantially determined by the accuracy of thephase angle measurement with the highest measuring frequency because thewavelength is the smallest here. The following formula applies:path change=phase angle change×wavelength/180°

The piston position measurement by means of a microwave is based uponthe following principle: An electromagnetic wave of an appropriatefrequency is coupled into the cylinder. The cylinder itself acts as aline structure for the wave. The wave passes in the cylinder to thepiston as a reflective member. On the piston the electromagnetic wave islargely reflected because the piston behaves electrically similarly to ashort circuit. The reflected wave runs back to the cylinder and isuncoupled from the cylinder again by means of the same structure bymeans of which the coupling also took place. The phase angle between thecoupled and the reflected signal is measured. If the piston changes itsposition, the path over which the electromagnetic wave passes within thecylinder also changes. The path change also brings about a change to thesignal duration and so also another phase angle between an incoming andreflected wave. Therefore, the phase between the incoming and returningsignal can be used as a measure for the piston position. The followingcorrelation between the piston position and the phase angle q results:

$\varphi = {\frac{2x \times 360{^\circ}}{\lambda} + \varphi_{o}}$

φ_(o) here is a phase offset which is mainly determined by the supplyand the coupling. It is constant and so has no effect upon the actualposition measurement. The above equation also gives the required phasemeasurement accuracy in order to be able to achieve a pre-specifiedposition measurement accuracy.

Since with a phase measurement one can basically not distinguish betweena phase angle φ and φ+n*360°, when using just one frequency onlycylinders up to a maximum piston stroke <λ/2 could be measured. Whenusing two or more frequencies it is possible, however, to measurepistons with a substantially greater length. With two frequencies thetwo wavelengths must not differ too greatly. For a cylinder with length1 the following applies for the wavelengths:

$\lambda_{1} > \lambda_{2} > \frac{2/\lambda_{1}}{2/{+ \lambda_{1}}}$

Since the phase angle of the reflected signal can not be measureddirectly and so the voltage measured on a mixer outlet is not directlyproportional to the piston position, an appropriate algorithm is usedfor the position search. Since the output signal is periodicallyrepeated, it must be ensured above all that the position search runsclearly, i.e. it must be possible to determine clearly in which periodthe piston is located. One possibility for determining the position isto record many measured values during one frequency sweep. Thesemeasured values are then transformed by means of a FFT or DFT into thefrequency range. From the position of the maximum of the spectrumproduced the position of the piston can then be determined. Ifsub-sampling when recording the measured values is not allowed with thismethod no problems associated with ambiguity can occur. By means of thismethod values for the piston positions are obtained without recording aposition table. Disadvantageous is the fact that on the one hand arelatively large number of measurement points have to be recorded, andthat the time required for calculation is relatively great.

Another possibility is to measure with only a few frequencies and todetermine the piston position by means of position tables. The measuredvalues are thus compared easily with the values of the points of theposition table. The position established then corresponds to the tablevalue which is most similar to the measured values. It is a disadvantagewith this method that ambiguities may occur. Since direct phasemeasurement is not implemented, clarity can not be guaranteed byobserving the condition described above. More precise investigationsshow that when using just two measuring frequencies there are alwayspoints with identical measured values if the cylinder is longer thanλ/2.

Since in practice this is mostly the case, at least three frequenciesmay be used. If the three measuring frequencies are chosen wisely, thereare then no more positions with which all three measured values areidentical. However, in practice the measured values must differ by aminimum amount at two piston positions in order to be able to guaranteeclarity, even with certain measuring errors. Therefore, with largercylinder lengths in particular the use of more than three frequenciescan be advantageous. Moreover, in this way the measuring accuracy isalso increased because noise or measuring errors which only occur withone frequency are suppressed.

The transmitted and received signals are generated in corresponding HFelectronics. For this purpose the coax conductor (=pin of the monopole)is connected via a solder joint, plug or bond connection which carriesthe HF electronics to the conductor board. The HF electronics 20 are inthe form of a single chip substrate made e.g. of silicium germanium. Thecomponents which are provided here are shown by the block diagram, HFchip. An oscillator (VCO=voltage controlled oscillator) generates thehigh frequency signal, e.g. with 24 GHz. The oscillator frequency isstabilized by a control loop. For this purpose the oscillator outputsignal is split into the frequency, e.g. by factor 16 and adjusted withquartz accuracy by means of a PLL. In the transmission branch there isthen a switchable divider which establishes the final transmissionfrequency by means of the divider ratio. With an oscillator frequency of24 GHz this can be 12, 6, 3, . . . GHz. The associated power amplifiercorresponding to the frequency is activated by an external circuitaccording to the chosen divider ratio. The signal is then radiated viathe monopole antenna. After the electromagnetic wave has been reflectedon the reflective member, it is received via the monopole antenna andforwarded to the receiver via two directional couplers. The receiver isin the form of an IQ receiver. According to the frequency set theintermediate frequencies of the receiver (IF out) undergo analog/digitalconversion and are analyzed in an FPGA (free programmable gate array).Consequently the distance value between the sensor and the piston areobtained. The latter is passed either analoguely e.g. via a 0 to 20 mAor 0 to IOV interface or digitally e.g. CAN bus to a SPS. In the FPGAthe function blocks DSP (digital signal processor), parts of theinterface, memory and parts of the PLL control are provided.

It should basically be emphasized that the principle of end positiondamping can be implemented in reverse in the sense of a kinematicreversal, i.e. the moveable plastic ring is located in the cover and theconically extending plastic pin on the outer surface of the cup.

According to FIG. 13 a-d a sequence of the reflective member at an endposition of the reflective member with the feed block is shown. Here theimplementation of the pneumatic end position damping when using theintegrated microwave sensor is primarily described, and in particular incontrast to the previously described implementation with central dampingwhich is not possible because the microwave antenna or the couplingprobe for feeding a transmission signal sits here. At this point it isemphasized that this type of damping can also be used, however, forcylinders without microwave sensor systems.

The basic structure characteristically shows a centrally positionedcoupling probe, a reflective member in the form of a cup piston with abase plate and an attached collar and a plunging region for the cuppiston in the cylinder floor provided as a recess in the feed block.

FIG. 13 a shows functionally how the cup piston approaches the cylinderfloor. In FIG. 13 b the piston engages in the plunge region of thecylinder floor and closes the air seal in the recess by means of thesealing ring so that upon further movement of the piston overpressure isestablished in the recess of the feed block. In FIG. 13 c a snap-shot isshown in which the piston is moved into the plunge region of the recess,and the overpressure in the region around the coupling probe is slowlybroken down by a bypass borehole that is also provided. In FIG. 13 d itis shown how the cup piston is moved out by applying pressure to thecylinder floor, and the air seal opens. Around the air seal compressedair can flow into the cylinder and exert force over the whole pistonregion.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its scope. Dimensions, types of materials,orientations of the various components, and the number and positions ofthe various components described herein are intended to defineparameters of certain embodiments, and are by no means limiting and aremerely exemplary embodiments. Many other embodiments and modificationswithin the spirit and scope of the claims will be apparent to those ofskill in the art upon reviewing the above description. The scope of theinvention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Moreover, in the following claims, theterms “first,” “second,” and “third,” etc. are used merely as labels,and are not intended to impose numerical requirements on their objects.Further, the limitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. §112, sixth paragraph, unless and until such claimlimitations expressly use the phrase “means for” followed by a statementof function void of further structure.

Key to Figures: FIG. 1   microwave stimulation piston and piston rod(principle)  piston appendage and reflective member  with optionalproperties FIG. 2 Components        Optional:       inlet and outletchannel       for end position       damping     pneumatic inlet andoutlet  collar base plate   end position damping     dielectricrestraint system       dielectric holding       screws    pistonappendage      monopole stimulation system (multi-      stage); couplingprobe     seal 2 piston appendage with optional properties: 2a; stopsafeguard without endposition damping and electric target  groovestructure 2b: stop safeguard with end position damping and electrictarget piston and piston rod (principle) 2c: stop safeguard with endposition damping and without electric target FIGS. 3, 4, 6 and 8Components FIG. 9 microwave sensor electronics I/F     metal FIG. 10digitate Steuersignale = digital control signals Referenztakt (zB. . . .) = reference cycle (e.g. . . . ) Steuerfeitungrnodule N Teller =control line modules N dividers Zylindereinkopplung = cylinder couplingBlockschaltbild HF chip = block diagram HF chip FIGS. 11 and 12 Priorart

What is claimed is:
 1. A distance measuring device comprising: analysiselectronics and a sensor device which has at least one coupling probefor feeding a transmission signal into a line structure and with areflective member disposed in the line structure which has a base platewith an attached collar forming a cup-shaped element; and a feed blockwith a recess into which the collar plunges, the recess having a sealingring which produces airtightness with the collar, wherein the attachedcollar is provided on the front face with a plastic plate; and anannular element formed from a plastic ring that includes the collar inan end position and configured to provide an end position damping. 2.The distance measuring device according to claim 1, wherein the attachedcollar comprises the coupling probe in an end position of the reflectivemember.
 3. The distance measuring device according to claim 1, furthercomprising a groove structure in a front face of the base plateextending in a circumferential direction.
 4. The distance measuringdevice according to claim 3, wherein the groove structure includes atleast two grooves.
 5. The distance measuring device according to claim3, wherein the groove structure includes a plurality of the groovesfilled with dielectric material.
 6. The distance measuring deviceaccording to claim 1, wherein the line structure is a circular hollowconductor, including a cylinder with a piston as a reflective member andthe plastic ring is mounted in a cover of the cylinder and configured tomove axially.
 7. The distance measuring device according to claim 1,further comprising an annular element formed from a plastic ringprovided on an outer surface of the collar and having a surface pairingcorresponding to an outer surface of the collar and extends conically inorder to provide end position damping.
 8. The distance measuring deviceaccording to claim 1, wherein the line structure is a circular hollowconductor, including a cylinder with a piston as a reflective member. 9.The distance measuring device according to claim 8, wherein thereflective member is attached to the piston.
 10. The distance measuringdevice according to claim 1, wherein the coupling probe comprises amonopole stimulation system, and the feed of a electromagnetic waveimplemented coaxially and converted to the monopole via a multi-stepcoaxial transformation.
 11. The distance measuring device according toclaim 1, wherein the coupling probe comprises a three-steptransformation module having a level base on the center of which acylinder is provided to which a pin is attached and wherein a feedregion is connected to the coupling probe.
 12. The distance measuringdevice according to claim 11, wherein the coupling probe is covered by aplastic material with low water absorption and water release.
 13. Thedistance measuring device according to claim 12, wherein the plasticmaterial comprises a PPS Gf 40 material.
 14. The distance measuringdevice according to claim 1, wherein the line structure includes a feedblock with a feed region that connects an HF transceiver to a dielectricrestraint system with the coupling probe via a wave guide.
 15. Thedistance measuring device according to claim 14, wherein the dielectricrestraint system is formed from a material with low water absorption andrelease and configured to be implemented in one of solidly and inindividual supports with cylinders with a large diameter.
 16. Thedistance measuring device according to claim 14, wherein pneumaticpressure compensation is provided.
 17. The distance measuring deviceaccording to claim 14, wherein the feed block includes boreholes intowhich the restraint system, the coupling probe and the coaxial feedregion are configured to be inserted.
 18. The distance measuring deviceaccording to claim 1, wherein the transmission signal is fed as anelectromagnetic wave in a high frequency range via the coupling probe.19. The distance measuring device according to claim 18, wherein theelectromagnetic wave is in a high frequency range of between about 100MHz and about 25 GHz.
 20. The distance measuring device according toclaim 1, wherein at least two transmission signals are radiated aselectromagnetic waves with different frequencies via the coupling probe.21. The distance measuring device according to claim 20, wherein thecoupled electromagnetic wave has monomodal propagation in the TEM modewith a coaxial structure.
 22. The distance measuring device according toclaim 20, wherein the coupled electromagnetic wave has monomodalpropagation in the E01 mode with the circular hollow conductor.
 23. Thedistance measuring device according to claim 1, wherein the sensordevice includes high frequency electronics with a transmitting andreceiving branch.
 24. The distance measuring device according to claim23, wherein the high frequency electronics comprises a PLL, anoscillator (VCO), a mixer, frequency distributors and amplifiersintegrated onto a common substrate.
 25. The distance measuring deviceaccording to claim 24, wherein the common substrate material being atleast one of silicium germanium, silicium, silicium germanium carbideand silicium carbide.
 26. The distance measuring device according toclaim 1, wherein at least one of the analysis electronics and the sensordevice being provided as interface electronics in a chip arrangement onthe feed block.
 27. The distance measuring device according to claim 26,wherein the transmitting and receiving frequency of the chip arrangementis selectable by adjusting a divider ratio by applying an externalvoltage in discrete steps.
 28. The distance measuring device accordingto claim 1, wherein the analysis electronics comprises a DSP, a PLL, andmemory implemented as a Free Programmable Gate Array (FPGA).
 29. Thedistance measuring device according to claim 28, wherein the interfaceelectronics are implemented with analog and digital operations and atleast a portion of the FPGA is allocated to the generation of aninterface protocol and control of digital to analog conversion.
 30. Thedistance measuring device according to claim 1, further comprising abypass borehole provided in the feed block.
 31. The distance measuringdevice according to claim 1, wherein the line structure is a circularhollow conductor, including a cylinder with a piston as a reflectivemember with the plastic ring mounted onto a front face of the cup-shapedelement.
 32. The distance measuring device according to claim 31,wherein a conical extension of rod of the piston is on the reflectivemember.
 33. The distance measuring device according to claim 1, whereinthe plastic ring is coupled to an outer surface of the cup-shapedelement and a cover plunge surface is formed conically and coated inplastic.
 34. The distance measuring device according to claim 1, furthercomprising a dielectric secondary ring configured as a stop safeguardfor the reflective member when the reflective member is moving.
 35. Thedistance measuring device according to claim 1, wherein the linestructure is a circular hollow conductor, including a cylinder with apiston as a reflective member, with the plastic ring mounted in a coverof the cylinder, an internal diameter of the plastic ring complementaryand received within an external diameter of a conical piston rodattachment of the piston.
 36. The distance measuring device according toclaim 35, wherein the plastic ring is mounted in the cover to allowaxial movement thereof.
 37. A method for determining a distance using adistance measuring device, the method comprising: providing a linestructure reflection which has a feed block with a feed region whichconnects a high frequency (HF) transceiver to a dielectric restraintsystem with a coupling probe via a waveguide, and providing a reflectivemember with a base plate with an attached collar for forming acup-shaped element; providing an annular element formed from a plasticring that includes the collar in an end position and configured toprovide an end position damping; and measuring a distance between a feedpoint defined by the coupling probe and the reflective member, whereinat least two transmission signals as electromagnetic waves withdifferent frequencies are coupled via the coupling probe.
 38. The methodaccording to claim 37, further comprising measuring the distance using aphase difference between the transmitted signal and the received signalof the electromagnetic wave.
 39. The method according to claim 38,wherein the difference with at least two transmission frequencies of therespective electromagnetic wave is about one percent of the absolutevalue, to cover a large measuring range.
 40. The method according toclaim 37, wherein the transmission signals are continuously radiated.41. The method according to claim 37, wherein three transmission signalsare radiated as electromagnetic waves via the coupling probe.
 42. Themethod according to claim 37, wherein the recess includes a sealing ringwith which the collar provides airtightness.
 43. The method according toclaim 37, wherein the difference between the frequencies of thetransmission signal of the respective electromagnetic wave is abouttwenty percent the absolute value, to achieve high interferenceresistance.
 44. The method according to claim 37, wherein a feed blockis provided with an annular recess into which the collar plunges. 45.The method according to claim 44, wherein a bypass borehole is providedin the feed block.
 46. A reflective member for a distance measuringdevice having analysis electronics and a sensor device which has atleast one coupling probe for feeding a transmission signal into a linestructure and with a reflective member disposed in the line structurewhich has a base plate with an attached collar forming a cup-shapedelement, and a feed block with a recess into which the collar plunges,the recess having a sealing ring which produces airtightness with thecollar, wherein the attached collar is provided on the front face with aplastic plate, wherein the reflective member is configured to reflect ahigh frequency (HF) signal and has a base plate with an attached collarfor forming the cup-shaped element, and further comprising an annularelement formed from a plastic ring that includes the collar in an endposition and configured to provide an end position damping.
 47. Thereflective member according to claim 46, wherein the attached collarincludes a plastic plate.
 48. The reflective member according to claim46, wherein a front face of the base plate comprises a groove structurethat extends in a circumferential direction.
 49. The reflective memberaccording to claim 48, wherein the groove structure includes a pluralityof grooves filled with dielectric material.
 50. The reflective memberaccording to claim 46, wherein the groove structure includes at leasttwo grooves.
 51. The reflective member according to claim 46, furthercomprising an annular element provided as a plastic ring, the annularelement on an outer surface of the collar.